Photovoltaic soil monitoring system with automated clean referencing system

ABSTRACT

A solar panel cleaning system includes: an automated cleaning device for cleaning a surface of a reference cell panel; a cleaning device controller in communication with a motor of the automated cleaning device, the cleaning device controller configured to receive a signal corresponding to measurement of a current of photovoltaic system. The cleaning device controller activates the automated cleaning device to clean a surface of the reference cell panel when the received signal indicates that a measurement of the current of the photovoltaic system is to be taken.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims priority to and is a continuation of pendingU.S. patent application Ser. No. 15/905,870 entitled “Soil MonitoringSystem” and filed on Feb. 27, 2018, now U.S. Pat. No. 10,243,514, whichclaims priority to and is a continuation-in-part of U.S. patentapplication Ser. No. 15/173,821 entitled “Soil Monitoring System” andfiled on Jun. 6, 2016, U.S. Provisional Patent Application Ser. No.62/273,267 entitled “Soil Monitoring Platform for Photovoltaic Panels”and filed on Dec. 30, 2015, U.S. Provisional Patent Application Ser. No.62/254,401 entitled “Automated System for Cleaning a PV Reference Panel,Single Piece of Glass, or Other Suitable Surface” and filed on Nov. 12,2015, U.S. Provisional Patent Application Ser. No. 62/216,257 entitled“PV Soil Monitoring Platform” and filed on Sep. 9, 2015, and U.S.Provisional Patent Application Ser. No. 62/171,187 entitled “Solar PanelSoiling Monitoring System” filed on Jun. 4, 2015, the contents of whichare hereby incorporated by reference in their entireties. Thisapplication also claims priority to U.S. Provisional Patent ApplicationSer. No. 62/590,267 entitled “PV Soil Monitoring System” and filed onNov. 22, 2017, U.S. Provisional Patent Application Ser. No. 62/571,461entitled “PV Soil Monitoring System with Automated Clean ReferenceEnclosure” and filed on Oct. 12, 2017, the contents of which are herebyincorporated by reference in their entireties.

FIELD

This disclosure relates to the field of photovoltaic panels. Moreparticularly, this disclosure relates to a solar panel soilingmonitoring system for monitoring reduced power generated by solar panelsas they become contaminated by dust and dirt.

BACKGROUND

Solar panels utilize energy from the sun and convert the sun's energy toelectrical power. It is important for solar panels to remain clean tomaximize production from the solar panels. Cleaning large-scalephotovoltaic (PV) plants or rooftop commercial PV plants can beexpensive. Further, it is important to understand the required frequencyand timing of cleanings to optimize performance of the PV plant and tominimize costs.

Traditional methods to measure loss of energy due to soiling of the PVsystem include measuring a combination of voltage and current for aspecified PV panel or panels in reference to a clean PV panel. However,due to the fact that standard PV panels consist of a plurality ofseries-connected PV cells these measurements are limited in accuracy andare lacking in the detailed analysis of the patterns of soiling in a PVsystem. Alternative methods have been developed to measure soilinglevels by measuring the differences in current and voltage on two singlecell pv reference panels. However, these methods lack the characteristiceffects of soiling that are specific to a PV panel consisting of aplurality of cells mounted inside a standard PV module. The presentinvention seeks to solve this problem by connecting each cell of aplurality of pv cells to a Measurement Unit (FIGS. 1, 6), whereby theIsc of each cell can be measured individually providing detailedinformation regarding the effects of soiling at each part of the pvpanel.

PV Reference Cells are typically used to establish an irradiancebaseline for PV plants. The irradiance measurements provided by PVReference Cells are used in the calculation of important performancemetrics such as Performance Ratio, for PV plants of all types and sizes.A current measurement of the PV cell typically is measured at regularintervals throughout the day and in the same plane of array (POA) as thenative PV panels. In this way, the PV Reference Cell provides aperformance an irradiance baseline that is used to calculate theperformance of the native PV system to determine if the PV system isoperating to expectation.

PV reference cells are often calibrated regularly according to rigorousstandards to ensure accuracy of the reference cells. The accuracy andreliability of this irradiance baseline is extremely important to themodeling, monitoring and operation of the PV plant, in order to find anddiagnose problems and ensure that the PV system is being operatedaccording to and O&M contract, as well as to ensure performance targetsare being met.

However, dirt and other debris collect on the surface of the PVreference cells over time and cause discrepancies in the measurements ofthe PV reference cell. Often the contribution of soiling on the PVpanels is overlooked due to the fact that the PV reference cells arethemselves not clean and therefore include the soiling loss in thebaseline irradiance measurements.

The common method for cleaning PV Reference Cells requires sending atechnician to the PV plant to wipe off the cell periodically. This isboth costly and impractical for the majority of PV plants, which areoften located in remote locations.

Automated methods for remote cleaning of the PV Reference Cell are notreadily available and tend to include complex methods that are bothunreliable and/or require additional maintenance.

What is needed, therefore, is solar panel soiling monitoring system formonitoring reduced power generated by solar panels as they becomecontaminated by dust and dirt.

SUMMARY

The above and other needs are met by a solar panel monitoring system formeasuring soiling losses in a photovoltaic system. In a first aspect, asolar panel soiling monitoring system for a photo-voltaic (PV) system isprovided, the monitoring system including: a soil monitoring panelincluding a plurality of arranged photovoltaic cells arranged on arectangular frame and connected in series to one another; a measurementunit including a circuit board in electronic communication with aswitchbox for controlling measurements of each of the plurality ofphotovoltaic cells of the soil monitoring panel, the measurement unit inelectronic communication with each of the plurality of photovoltaiccells of the solar monitoring panel; a communication unit in electroniccommunication with the measurement unit and including a device fortransmitting a detected short circuit current of each individualphotovoltaic cell of the plurality of photovoltaic cells; and a datastorage system in electronic communication with the communication unitincluding a processor, a computer readable storage medium, and one ormore computer programs operable on the data storage system. The datastorage system determines soiling conditions of the soil monitoringpanel based on measured short circuit currents of each of the pluralityof photovoltaic cells of the soil monitoring panels.

In one embodiment, the solar panel monitoring system includes areference solar panel which may be installed on the same glass substrateas the Solar Monitoring panel and includes at least one photovoltaiccell in electronic communication with the measurement unit and or dataacquisition system, wherein the measurement unit receives a shortcircuit current measurement of the at least one photovoltaic cell of thereference solar panel and wherein the data storage system furtherdetermines conditions of the soil monitoring panel based on comparedmeasured short circuit currents of each of the plurality of photovoltaiccells of the soil monitoring panel and the at least one photovoltaiccell of the reference solar panel.

In another embodiment, the reference solar panel is positioned at thesame azimuth and elevation angle as the soil monitoring panel and ontothe same glass substrate as the Soil Monitoring panel.

In yet another embodiment, the reference solar panel further comprisesan automatic Clean Reference system, which includes one or more movablecleaning components and a protective outer cover which covers and sealsthe PV reference cell(s) from environmental contaminants, when not inuse. The Clean Reference System consists of a motor control unit whichis in electronic communication with the DAS, wherein the controlleractivates the motor to open or close the Reference Cell Cover andhermetically seal the pv reference cell from exposure to outsidecontaminants.

In one embodiment, the solar panel monitoring system further includesone or more environmental condition sensors and PV String sensors, inelectronic communication with the data storage system, communicationsunit, and/or measurement unit, and the one or more environmentalcondition and or PV string sensors selected from the group consisting ofa PV string voltage, PV string current, temperature sensor, rain ormoisture sensor, and a wind sensor.

In yet another embodiment, the solar panel monitoring system furtherincludes a communications module, in electronic communication with thedata acquisition system for communicating with a remote server database.

In one embodiment, the solar panel monitoring system further includes acommunications module, in electronic communication with the remoteserver.

In one embodiment the solar panel monitoring system includes a chargecontroller in electronic communication with one or more PV cells of theSoil Monitoring Panel and or PV Reference Cell Panel and which performsthe function of charging a local battery with the power from the PVcells, when the PV cells are not being measured.

In yet another embodiment, the solar panel monitoring system includes aforecasting module implemented on the data storage system and or RemoteServer, wherein the forecasting module determines a cleaning schedule ofa photovoltaic system based on a determined soiling rate of the soilmonitoring panel.

In a second aspect, a method of determining a soiling condition of aphoto-voltaic system is provided, the method including: (1) providing asoil monitoring panel having a plurality of arranged photovoltaic cells;(2) providing a measurement unit in electronic communication with eachof the individual photovoltaic cells of the soil monitoring panel; (3)providing a data acquisition system including a processor, a computerreadable storage medium, and one or more computer programs operable onthe data acquisition system; (4) providing a communications unit (FIG.1, 6), for communicating with a server database; (5) measuring a shortcircuit current of each of the individual photovoltaic cells via theswitchbox on the measurement unit; (6) comparing measured short circuitcurrents of each of the individual photovoltaic cells with other of theindividual photovoltaic cells of the soil monitoring panel and aReference Panel; and (7) determining soiling conditions of the soilmonitoring panel based on measured and compared short circuit currentsof the individual photovoltaic cells with a Reference Panel.

In one embodiment, the method of determining a soiling condition of aphoto-voltaic system further includes: providing a reference solar panelincluding at least one reference photovoltaic cell, which may be mountedonto the same glass substrate as the plurality of pv soil monitoringcells; measuring a short circuit current of the at least one referencephotovoltaic cell and storing the results on the data storage system;comparing measured short circuit currents of each of the individual soilmonitoring photovoltaic cells with the measured short circuit current ofthe reference photovoltaic cell; determining soiling conditions of thesoil monitoring panel based on measured and compared short circuitcurrents of the individual photovoltaic cells and the referencephotovoltaic cell.

In one embodiment, the method of determining a soiling condition of aphotovoltaic system further includes: providing an Automated CleanReference System including an enclosure which is driven by a motorprotect the Reference Cell Panel by enclosing the surface of theReference Cell Panel and thereby sealing the surface of the reference pvcell(s) from exposure to Dust and debris, in-between measurements.

In a third aspect, a solar panel monitoring system is providedincluding: a soil monitoring panel including a plurality of arrangedphotovoltaic cells; a dedicated reference cell with automated cleanreference system, a measurement unit including a circuit board inelectronic communication with each of the plurality of photovoltaiccells of the soil monitoring panel and the photovoltaic reference cell;a communications unit (FIG. 1, 6), for receiving a short circuit currentfrom each individual photovoltaic cell of the plurality of photovoltaiccells of the soil monitoring panel and the reference panel; and a dataacquisition system including a processor, a computer readable storagemedium, and one or more computer programs operable on the dataacquisition system; a reference solar panel including at least onephotovoltaic cell in electronic communication with the data acquisitionsystem, wherein the data acquisition system receives a short circuitcurrent of the at least one photovoltaic cell of the Soil Monitoringpanel and the pv reference panel, and wherein the data acquisitionsystem further determines conditions of the soil monitoring panel basedon compared measured short circuit currents of each of the plurality ofphotovoltaic cells of the soil monitoring panel and the at least onephotovoltaic cell of the reference solar panel. The data acquisitionsystem receives a short circuit current of at least one photovoltaiccell of the reference solar panel and a short circuit current of each ofthe plurality of arranged photovoltaic cells of the soil monitoringpanel. The data acquisition system determines conditions of the soilmonitoring panel based on compared measured short circuit currents ofeach of the plurality of photovoltaic cells of the soil monitoring paneland the at least one photovoltaic cell of the reference solar panel.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, aspects, and advantages of the present disclosure willbecome better understood by reference to the following detaileddescription, appended claims, and accompanying figures, wherein elementsare not to scale so as to more clearly show the details, wherein likereference numbers indicate like elements throughout the several views,and wherein:

FIG. 1 schematic diagram of a solar panel soiling monitoring systemaccording to one embodiment of the present disclosure;

FIG. 2 is a top perspective view of a soil monitoring panel with areference cell panel arranged on the side of the soil monitoring panelaccording to one embodiment of the present disclosure;

FIG. 3 is a bottom view of a soil monitoring panel with a reference cellpanel arranged on the side of the soil monitoring panel according to oneembodiment of the present disclosure;

FIG. 4 is a close-up view to a top of the reference cell panel showingmechanical arrangement of a sealing gasket frame mounted onto thesurface of the reference cell panel and the reference cell cover sealinggaskets mounted into the sealing gasket frame according to oneembodiment of the present disclosure;

FIG. 5 illustrates a configuration of a soil monitoring system installedat ends of a row of PV panels to measure the effects of soiling on theadjacent PV panels in the native PV array according to one embodiment ofthe present disclosure;

FIG. 6 is a block diagram of an electrical system including arelationship between soil monitoring cells, flexible PCB, measuringunit, DAS, and communications unit according to one embodiment of thepresent disclosure;

FIG. 7 shows top and bottom views of a soil monitoring panel andreference cell panel including a flexible PCB according to oneembodiment of the present disclosure;

FIG. 8 is a flow chart detailing a process of a clean cycle forecastsoftware tool used to determine an optimal cleaning cycle; and

FIG. 9 is a top perspective view of a soil monitoring panel with amovable cover panel according to one embodiment of the presentdisclosure.

DETAILED DESCRIPTION

Various terms used herein are intended to have particular meanings. Someof these terms are defined below for the purpose of clarity. Thedefinitions given below are meant to cover all forms of the words beingdefined (e.g., singular, plural, present tense, past tense). If thedefinition of any term below diverges from the commonly understoodand/or dictionary definition of such term, the definitions belowcontrol.

At the outset, it should be understood by one of ordinary skill in theart that embodiments of the present solar panel soiling monitoringsystem can include software or firmware code executing on a computer, amicrocontroller, a microprocessor, or a digital signal processor (DSP);state machines implemented in application specific or programmablelogic; or numerous other forms. Embodiments of a solar panel soilingmonitoring system of the present disclosure can include one or morecomputer programs, which include non-transitory machine-readable mediahaving stored thereon instructions that can be used to program acomputer (or other electronic devices) to perform processes according tothe presently claimed solar panel soiling monitoring system. Themachine-readable media can include, but is not limited to, floppydiskettes, optical disks, CD-ROMs, and magneto-optical disks, ROMs,RAMs, EPROMs, EEPROMs, magnetic or optical cards, flash memory, or othertype of media or machine-readable medium suitable for storing electronicinstructions.

Referring to FIG. 1 and FIG. 2, the solar panel soiling monitoringsystem includes a soil monitoring panel 10, clean reference solar panel8, and an automated clean reference system. The reference solar panelincludes 8 at least one, dedicated PV cell which is installed onto thesame glass sheet as the soil monitoring panel 10 (FIGS. 2-4 and 7),which is used to provide measurements of a soiled panel versus the cleanreference cell 8. The reference solar panel 8 may be mounted to eitherside of the soil monitoring panel 10 or on either extreme end of thesoil monitoring panel 10. Cleaning system control units are connected tothe automated clean reference system (FIGS. 1 and 6), which include anautomated enclosure system which retracts a cover 2 encapsulating thereference cell panel, when a soiling measurement is to be taken, therebyexposing the clean reference solar cell to the sun. The reference cellcover 2 may include a reference cell cover bleed valve 3 located on thereference cell cover. The solar soil monitoring panel 10 (having aplurality of PV cells) and reference cell panel (FIGS. 2-4 and 6-7) areconnected to a measurement unit (FIGS. 1 and 6) which providesmeasurement of the short circuit current (referred to herein as “Isc”)of a plurality of photovoltaic cells of the soil monitoring panel 10(FIGS. 2-3 and 6-7) individually and in coordination with a measurementof the Isc of the reference cell panel 8 (FIGS. 2-4 and 6-7). Themeasurement unit (FIGS. 1 and 6) is connected to one or more datastorage system (FIGS. 1 and 6) (i.e. EEPPROM). The measurement unit(FIGS. 1 and 6), may also be connected to a communications unit (FIGS. 1and 6). The data storage unit may be a separate third-party system (ie.Data Acquisition System (“DAS”)) consisting of a storage and controlsystem or may be integrated into the measurement and/or communicationsunits.

A number of environmental sensors including a relative humidity sensor,a temperature sensor, moisture sensor and a wind sensor, (amongstothers) may be connected to the DAS and or communications unit motorcontrol unit DAS and or measurement units, as shown in FIG. 1.

Additionally, a current/voltage sensor connected to the native PVsystem, as shown in FIGS. 1 and 5, may be also connected to the DASand/or measurement unit to relay current/voltage information about thenative PV system to the communications unit.

A normalization button (FIG. 1) may be connected to the communicationsunit of the soil monitoring panel 10 to recalibrate measurements to anormalized form periodically to ensure additional differences inperformance (ie. performance degradation over time) between thereference panel and solar panel cells are not included in the soilingcalculations. The Communications unit may have a connection to a modem,which exchanges the solar panel data and calculations between a remoteserver (FIG. 1) and the local data storage system. While the server, maybe remote, the remainder of the system, is considered to be located onthe site where the PV system losses are to be measured.

Electronic Enclosure

In one embodiment an electronics enclosure 5 (FIGS. 2 and 3) may house amotor controller 15 including a power supply and a motor 14. In anotherembodiment the electronics enclosure 5 may house the motor 14, motorcontroller 15, DAS, a temperature sensor, a charge controller, powersupply, a communications unit, and measurement unit.

The electronics enclosure 5 may be of a standard construction to thoseelectronic enclosures common in the field, rated for outdoor use, andconsisting of a rectangular box with two halves (top and bottom) whichare joined by removable screws. The bottom half of the electronicenclosure 5 (the side opposite the half with access to the removablescrews), may contain a small rectangular hole to provide a passage for aportion of a flexible PCB, into the electronics enclosure 5 where it canconnect directly to the measurement unit.

Soil Monitoring Panels

Embodiments of the present disclosure seek to solve the problems ofexisting systems by connecting each cell of a plurality of PV cells to ameasurement unit, whereby the Isc of each cell can be measuredindividually providing detailed information regarding the effects ofsoiling at each part of the PV panel.

The soil monitoring panel 10 may include a mounting frame 1 and anadjustable frame 9 (FIG. 2) proportional to those of standard solarpanels. The adjustable frame 9 may be adjustable in size in order tomatch the specific distance between the PV cells and the frame on agiven solar panel. Soiling typically accumulates on the bottom edges ofthe solar panel frame and builds upward (referred to as “edge soiling”).Once the soiling accumulation reaches the region directly over the PVcell, it begins to affect the light collection of the PV cell.Therefore, the distance between the PV cell and the panel frame can havea significant effect on the soiling losses. The distance between the PVcells and the panel frame can vary widely between manufacturers, whichfurther complicates measuring the effects of edge soiling on differentPV panel technologies. The current invention solves this issue byproviding an adhesive or mechanically adjustable superficial framesurrounding the surface of the soil monitoring panel so that thedistance between PV cells and panel frame are matched with the PV panelsof the native PV array.

Reference Cell Panel

The reference cell panel 8 may be without a frame to enable easycleaning by the automated clean reference system. The soil monitoringpanel 10 and the reference cell panel 8 may share a single glasssubstrate 26 with dedicated PV cells for soil monitoring and dedicatedcells for clean reference.

In another embodiment, the soil monitoring panel 10 and the referencecell panel 8 may consist of separate units which are mounted adjacent toeach other. The soil monitoring panel 10 may be connected to thereference cell panel 8 by the electronics enclosure 5 which extendsacross the bottom of the reference cell panel 8 and the soil monitoringpanel 10. In this way the reference cell panel 8 and the soil monitoringpanel 10 may be mounted to the electronics enclosure 5 using a standardadhesive, which ensures that the reference cell panel 8 and the soilmonitoring panel 10 are mounted adjacent to each other and at the sameelevation angle. In this way the reference cell panel 8 and the soilmonitoring panel 10 are connected to each other and function as a singleunit.

The current of a PV panel is directly proportional to the irradianceincident on the surface of the cells. As standard PV panels consist of aplurality of cells wired in-series, the current of the PV panel islimited to the current of the weakest cell in the series connectedstring of cells. In order to accurately measure losses due to soiling,and better understand the specific losses due to pattern soiling it isimportant to measure the short circuit current of each cell individuallyas it is situated inside the PV panel.

It is impossible to determine the pattern of soiling present on a PVpanel by only measuring the current of a series-connected PV panel. Inaddition, normalization is complicated by the PV cell mismatch which canlead to substantial errors in measurement on a standard PV panel. Byconnecting each cell of the reference cell panel 8 and the soilmonitoring panel 10 to a measurement unit, errors due to mismatchbetween PV cells can be eliminated, significantly improving the accuracyand reliability of the soiling loss measurements. Additionally, soilpatterns can be easily assessed to determine the specific soilinglosses, prevent hotspots, more accurately model the effects of soilingon different PV technologies and determine suitable cleaning techniques.As shown in FIGS. 1 and 6, the cells of the reference cell panel 8 andthe soil monitoring panel 10, are connected individually to themeasurement unit.

The cells of the reference cell panel 8 and the soil monitoring panel 10may also be connected in-series to provide power to a battery chargerfor autonomous power.

Measurement Unit

With respect to the measurement unit, a minimum of two panels of thetype described above one reference cell panel 8 and one soil monitoringpanel 10 are measured simultaneously. Each panel of the soil monitoringsystem (reference cell panel 8 and the soil monitoring panel 10) may beinstalled on a single glass substrate and connected to a singlemeasurement unit or each panel may be connected to a separatemeasurement unit dedicated to measuring the Isc of each panel.

In another embodiment, the reference cell panel 8 and the soilmonitoring panel 10 may be formed of separate units which are mountedadjacent to each other. In this case the soil monitoring panel 10 may beconnected to the reference cell panel 8 by the electronics enclosure 5which extends across a bottom of the reference cell panel 8 and the soilmonitoring panel 10. The reference cell panel 8 and the soil monitoringpanel 10 may be mounted to the electronics enclosure using a standardadhesive, which ensures that the reference cell panel 8 and the soilmonitoring panel 10 are mounted adjacent to each other and at the sameelevation angle. In this way the reference cell panel 8 and the soilmonitoring panel 10 are connected to each other and function as a singleunit.

Each cell of the reference cell panel 8 and the soil monitoring panel 10is connected to the measurement unit via the flexible PCB. A switchingcircuit inside the measurement unit will connect the measurement devicesto each cell in the reference cell panel 8 and the soil monitoring panel10. The measurement unit will measure the individual short circuitcurrent (Isc) from each cell in the soil monitoring panel 10 and thecorresponding cell or cells in a clean reference panel 8.

The measurement unit includes a microprocessor (MCU) in operablecommunication with analog-to-digital converter multiplexer, MOSFETtransistors and precision Hall sensors. In one embodiment of themeasurement unit includes a data storage system or data acquisitionsystem having a memory unit that will be included on the same printedcircuit board (PCB) as the switching circuits. In another embodiment,any third-party data storage system or DAS can be connected to themeasurement unit as a separate unit. Using these components, themeasurement unit upon a pulse signal from the DAS unit on a periodicbasis (e.g., one time per hour), automatically takes an instantaneousshort circuit current (Isc) measurements from each corresponding pair ofcells from the soil monitoring panel 10 and the clean reference 8.

In another embodiment, a switching circuit in the measurement unit canconfigure the cells in any combination of physical circuits (series andparallel) and measure the resulting lsc and or Voc of each circuit. Themeasurement unit then sends the measurements to a local storage devicewhich stores the resulting measurements from each pair of correspondingcells from the reference cell panel 8 and the soil monitoring panel 10or each pair of corresponding circuits from each respective panel.

SOILING Loss CALCULATIONS

After collecting the lsc measurements from each cell of each panel, ascript in the MCU of the DAS unit and/or measurement unit performs amathematical algorithm upon the individual measurements taken from eachcell to determine the following (but not limited to) additional soilingcharacteristics, such as average soiling loss percent (average loss ofall cells on soil monitoring vs. those on the clean reference solar)percent of non-uniformity of soiling, (delta between the weakest cell onthe soil monitoring panel and the strongest cell on the soil monitoringpanel 10), soiling losses from cells located in the corners of thepanel, the loss due to soiling on each row of cells and along theborders of the panel, the total soiling loss for the panel (weakest cellcurrent) and determination of any forward-biased bypass diodes.

A first program written into the MCU of the measurement unit or DAS unitor a remote server, is able to self-monitor the soil monitoring panel 10to determine if there are large differences in cell lsc values comparedto other cells in the same soil monitoring panel 10. In this way, thecapability exists to determine if the cells of the soil monitoring panel10 may have an aberration due to uncharacteristic spot soiling, such asan aberrant leaf or bird dropping, which may not be representative ofthe native soiling pattern in general. Using a user interface providedvia an Internet web application, the user is able to configure thealarms and calculations to include or ignore these aberrations to bettermatch the average soiling of the native PV system.

A second program written into the MCU of the measurement unit is alsoable to calculate the effects of active bypass diodes in the nativepanels. PV panels typically include 2 or 3 bypass diodes which help toprotect the PV panel from loss of current and/or damage to the PV cellsby redirecting current around weak or damaged cells. However, thenumber, and type of bypass diodes varies widely as well as the PV cellcharacteristics, which further complicates the measurement of theeffects of soiling on different PV panel technologies and manufacturers.The current invention solves this issue by using the lsc measurements ofeach cell, the PV cell resistance, and bypass diode configurations, tocalculate power lose due to active bypass diodes. In this way a closesimulation of the characteristic performance of the native PV panels ismaintained and the effects of soiling can be effectively modeled fordifferent PV panel technologies.

Bypass Diodes

For embodiments with bypass diodes included in the native photovoltaicpanels, the resulting effects of soiling on PV panels with bypass diodescan be measured by calculating the Voltage as a function of Isc andCharacteristic shunt resistance of each PV cell in the soil monitoringpanel 10. Differences in cell voltages between surrounding cells of thesoil monitoring panel 10 can be compared with the breakdown voltage ofdiodes of the native panels to determine when the diodes will be forwardbiased, thereby eliminating these cells from contributing any power(reducing the power of the panel by subtracting the power of each cellthat would be bypassed by the forward bypassed diode in the nativepanel). The loss of power due to active bypass diodes can be calculatedby subtracting the calculated power from each cell(s) of the soilmonitoring panel 10 affected by active bypass diodes.

Charging System

A battery and charge controller (FIG. 6) may be used to collect energyfrom the soil monitoring panel 10 and/or the reference panel 8 that isnot used during the measurement process to power the measurement unit,electronics (MCU, ADC, MOSFETs, and the like), eliminating the need forAC power connections and facilitating completely independent and remoteinstallation, if desired.

Automated Clean Reference System

The automated clean reference system of the present disclosure providesa fully automated, mechanism for protecting and maintaining a PVreference cell in a clean state to ensure a reliable performancebaseline. The device does not require any cleaning liquids, tubes,tanks, pumps, or nozzles.

The automated clean reference system described in this disclosure may beincluded as part of a PV soil monitoring system as described in thisdisclosure or may be used separately in order to maintain a referencebaseline.

The preferred embodiment of the automated clean reference systemincludes the following main components. Note that the components with *are included as part of the soil monitoring system as describedpreviously and may or may not be included in other embodiments of theautomated clean reference system.

Parts that make up the automated clean reference system include:

-   -   1. reference cell panel 8;    -   2. electronic enclosure 5;    -   3. reference cell cover 2;    -   4. motor(s) 14;    -   5. motor control system 15;    -   6. * data acquisition system (DAS) (FIG. 1);    -   7. temperature sensor (FIG. 1);    -   8. * charge controller (FIG. 6);    -   9. power supply (FIG. 6);    -   10. * communications unit (FIG. 6);    -   11. * measurement unit (FIGS. 1 and 6);    -   12. fixed brush 4;    -   13. reference cell cover drive screw 13;    -   14. drive screw cover 11;    -   15. reference cell cover drive bar 14;    -   16. reference cell cover sealing gasket 7;    -   17. mounting frame 1;    -   18. moisture sensor 6;    -   19. * soil monitoring panel 10;    -   20. toothed rails 30;    -   21. motor gearheads 32.

The DAS, charge controller, communications unit, measurement unit, andsoil monitoring panel 10 are included in the preferred embodiment asdescribed previously in the PV soil monitoring system above. In otherembodiments one or more of these components may not be included as partof the automated clean reference system.

In one embodiment, the reference cell panel 8 may be installed adjacentto a soil monitoring panel 10 and constructed on the same glasssubstrate as the soil monitoring panel 10. In another embodiment, thereference cell panel 8 may be installed on a separate glass substratefrom the soil monitoring panel 10.

In one embodiment the electronics enclosure 5 may house the motorcontroller 15, power supply and motor 14. In another embodiment theelectronics enclosure 5 may house the motor 14, motor controller 15,DAS, temperature sensor, charge controller, power supply, communicationsunit, measurement unit.

The electronics enclosure 5, may be of a standard construction to thoseelectronic enclosures common in the field, rated for outdoor use, andconsisting of a rectangular box with two halves (top and bottom) whichare joined by removable screws. The bottom half of the electronicenclosure 5 (the side opposite the half with access to the removablescrews), may contain a small rectangular hole to provide a passage for aportion of the flexible PCB, into the electronics enclosure 5 where itcan connect directly to the measurement unit.

A flexible printed circuit board is constructed of a thin flexiblematerial suitable for use in a PV panel. The flexible PCB is used in theconstruction of the soil monitoring panel 10 and reference panel 8 tosafely route electrical circuits from the PV cell busbars to themeasurement unit located in the electronics enclosure 5. The flexiblePCB may also provide connection between a PV soil monitoring panel 10and or reference cell panel 8 to the charge controller.

The bottom half of the electronic enclosure 5 (the side with therectangular shaped hole for the flexible PCB to pass) may be covered ina layer of adhesive in order to glue the electronic enclosure 5 to thebottom of the reference cell panel 8 and/or the bottom of the soilmonitoring panel 10.

The temperature sensor is connected to the bottom of the reference cellpanel 8 and to the DAS and/or measurement unit.

A portion of the electronic enclosure 5 houses the electronic motors 14and motor controller 15. The motors 14 are connected electrically to themotor controller 15, which is also connected to the power supply andDAS.

In one embodiment, the motors 14 may be oriented such that the motoraxle is facing downward away from the reference panel 10. The motor axlemay protrude through a hole in the top of the electronic enclosure 5where it is directly connected to the reference cell cover drive screw13, such as via a 90 degree gear. The reference cell cover drive screw13 is mounted along the bottom of one side of the electronics enclosure5 directly below the motor axle on the outside of the electronicsenclosure 5. A hole in the bottom of the electronics enclosure 5 issealed around the motor axle in order to ensure that no water orcontaminants are able to enter the electronics enclosure 5.

The reference cell cover drive screw 13 is protected from environmentalcontaminants (dust, water, etc.) by the drive screw cover 11. The drivescrew cover 11 is mounted to the bottom of the electronics enclosure 5in such a way as to encircle the perimeter of the reference cell coverdrive screw 13.

In one embodiment, a groove on either side of the drive screw cover 11is constructed so that the edges of either side of the reference coverdrive bar 14 can fit into the grooves in the drive screw cover 11 insuch a way as to completely enclose the reference cell drive screw 13when the reference cell drive bar 14 is fully retracted (in the closedposition).

The reference cell drive bar 14 is connected to the reference cell drivescrew 13 on the bottom of the electronics enclosure 5 using commonmounting hardware. The reference cell drive bar 14 is also fastened tothe reference cell cover 2 so that as the reference cell drive screw 13is turned by the motor the reference cell drive bar 14 movesforward/backwards laterally, forcing the reference cell cover 2 to alsoslide laterally (i.e. open and close) over a surface of the referencecell panel 8.

The reference cell drive bar 14 slides along a C channel groove oneither side of the reference cell cover 2 and provides a completeenclosure for the reference cell drive screw 13 when it is in the fullyclosed position.

In one embodiment the reference cell drive screw 13 is a helical screwwhich is used to attach a mounting bracket to drive a load in a lateraldirection as the screw turns. A 90 degree, rotational gear may be usedto translate the motion of the motor axle to the reference cell drivescrew 13.

In another embodiment the reference cell drive screw 13 may be a linearactuator which is used to drive a load in a lateral direction.

The reference cell cover 2 may consist of a any suitable material (i.e.glass, plastic, metal . . . etc.) which is mounted to the reference celldrive bar 14 on one side of the reference cell cover 2 using commonfasteners.

In one embodiment, as shown in FIG. 9, the reference cell cover 2 mayinclude toothed rails 30 on sides of the reference cell cover 2 in orderto drive the reference cell cover 2 between open and shut positions.

In another embodiment the motors 14 may be oriented such that the motoraxles are facing upwards toward the reference panel 10. A small hole oneither side of the electronic enclosure will provide a means for themotor axels to extend through the electronic enclosure 5 on either sideof the electronic enclosure 5. Motor gearheads 32 are mounted onto themotor axles in such a way that they are in direct contact with thetoothed rail 30 on either side of the reference cell cover 2.

The reference cell cover 2 may additionally include a sealing gasketframe 24 and or a inside sealing gasket 21 which is mounted to theinside of the reference cell cover 2 in such a manner as to be alignedwith the counterpart sealing elements of an outside sealing gasket 22.

The reference cell cover 2 may additionally include a fixed brush 4which may be mounted to the inside of the reference cell cover 2. Thefixed brush 4 may be of any suitable material or type so as to rid thesurface of the reference cell panel 8 of debris as the reference cellcover 2 is opened. The fixed brush 4 may be mounted on the inside of thereference cell cover 2 so that it hangs downward towards the surface ofthe reference cell panel 8 and comes in direct contact with thereference cell panel 8. In this way the fixed brush 4 clears a surfaceof the reference cell panel 8 as the reference cell cover 2 slideslaterally across the surface of the reference cell panel 8.

In one embodiment, the sealing gasket frame 24 may be mounted to the topsurface of the reference cell panel 8 and or the inside surface of thereference cell cover 2 in a such a way as to completely encircle theperimeter of the PV cell or cells provided in the reference cell panel8. The sealing gasket frame 24 consists of a rigid metal or plasticframe which provides a supporting structure for the inside sealinggasket 21 and/or the outside sealing gasket 22.

In another embodiment, the sealing gasket frame 24 may be constructedwith a C-shaped channel for inserting the rectangular shaped, bottomportion of the sealing gaskets 7 into the sealing gasket frame 24. Thesealing gasket frame 24 may also contain a series of screw holes in thebottom portion of the frame for fixing the sealing gaskets 7 to thesealing gasket frame 24. In this way the sealing gasket frame 24 alsoprovides a means for easy installation and replacement of the sealinggaskets 7.

The sealing gasket frame 24 may be mounted to the reference cell panel 8and/or the reference cell cover 2 using an adhesive or fastenersstandard in the trade. The sealing gasket frame 24 provides a permanentrigid frame around the perimeter of the reference cell cover 2 and orthe perimeter of the reference cell panel 8, where the outside sealinggaskets 22 and/or the inside sealing gaskets 21 can be installed into orremoved from, the C-channel of the sealing gasket frame 24 and fixed orremoved into the sealing gasket frame 24 by a gasket frame set screw 23which is provided on the side of the sealing gasket frame 24. Thisprovides for easy assembly of the reference cell cover 2 as well as ameans of replacing the outside sealing gaskets 22 and inside sealinggaskets 21 in the case that they become sufficiently worn.

A portion of the inside sealing gasket 21 is designed to fit inside aC-channel grove provided by the outside sealing gasket 22, whichprovides support for the reference cell cover 2 as it is extended beyondthe edge of the reference cell panel 8 and also provides a continuous,hermetic seal between the reference cell cover 2 and the top surface ofthe glass of the reference cell panel 8 when the sealing gaskets 7 areforced together by the closing motion of the reference cell cover 2.

The inside sealing gaskets 21 and outside sealing gaskets 22 may be ofany shape or material which is commonly used to create a hermetic sealbetween the reference cell cover 2 and the reference cell panel 8 whenthe reference cell cover 2 is in the completely closed position over thereference cell panel 8.

The reference cell panel 8 is electrically connected to the measurementunit, DAS, and temperature sensor. The temperature sensor is connectedto the DAS. The power source is connected to the DAS, temperaturesensor, the motor controller 15, and communications unit. The motorcontroller 15 is connected to the motor 14.

In one embodiment, the PV cells of the reference cell panel 8 and/or thesoil monitoring panel 10 may be connected in-series to a chargecontroller and battery when the PV cells are not needed for soilingmeasurements. In this way the PV cells provide autonomous power withoutthe need for remote power sources.

In one embodiment, the moisture sensor 6 is mounted in the same plane asthe reference cell panel 8 on the outside of the electronics enclosure5. The moisture sensor 6 may be electrically connected to the DAS andpower supply. The moisture sensor 6 provides indication of wet weatherconditions (i.e. rain) to determine if the protective reference cellcover 2 should be opened, thus exposing the clean reference cell panel 8to potential environmental contaminants (i.e. water and contaminantscontained therein), which might undermine the accuracy of the soilingmeasurements. If for example, the moisture sensor detects that water ispresent on the panel, the reference cell cover 2 may remain in theclosed position to avoid exposing the reference cell panel 8.

The communications unit may be connected to the DAS and/or themeasurement unit.

In one embodiment, the communications unit, DAS and measurement unit,charge controller, power source, may be separate units located outsideof the electronics enclosure 5 or inside the electronics enclosure 5.

In one embodiment the moisture sensor 6 may be mounted on the top of theelectronics enclosure 5 and is electrically connected to the DAS andpower supply.

In another embodiment, additional environmental sensors (such ashumidity, wind speed . . . etc.) may be electrically connected to theDAS and power supply.

Function of the Automated Clean Reference System

The reference cell panel 8 is installed in the same plane of array asthe native PV panels so as to best match the conditions of the native PVpanels. Typically the reference cell panel 8 and soil monitoring panels10 are installed on a single glass substrate, which is mounted alongsidethe native PV array at the end of a row of PV panels. The general intentof the PV reference cell enclosure system is to keep the reference cellpanel 8 in a sealed enclosure in between measurements to prevent theaccumulation of dust and/or dirt onto the surface of the reference cellpanel 8 and in this way maintain a reliable and clean reference forsoiling measurements.

The motorized reference cell cover 2 is controlled by the motor 14 whichis controlled by the motor controller 15 so that it only opens to exposethe reference cell panel 8 a brief time when taking a measurement of thereference cell panel 8. Before and after the measurements are taken thereference cell cover 2 is closed in order to protect the reference cellpanel 8 from further exposure to outside contaminants.

Before any measurements are taken, the moisture sensor 6 may be firstmeasured and sent to the DAS and/or communications unit to detect thepresence of water on the surface of the reference cell panel 8 whichwould indicate water (i.e. rain). Additional environmental sensors (i.e.humidity, wind speed . . . etc.) may also be connected to the DAS todetect the presence of adverse conditions for measurements. Themeasurements are calculated and compared against stored thresholds. Ifthe measurements exceed a given threshold it would indicate that adverseconditions exist (i.e. rain or excessive wind) and the enclosure may notbe opened in order to avoid exposing the reference cell panel 8 toenvironmental contaminants.

Upon receiving a signal from the communications unit, DAS and/or motorcontroller 15, the motor 14 rotates translating the motion to thereference cell drive screw 13. A common fastener attaches to thereference cell drive screw 13 and the reference cell drive bar 14 and inthis way translates the circular motion of the motor to a lateralmotion, which moves the reference cell cover 2 laterally in order toopen and close the reference cell cover 2 which is attached to thereference cell cover drive bar 14 and thus exposes the reference cellpanel 8 to unobstructed sunlight.

In one embodiment, the fixed brush 4 may be connected to the inside ofthe reference cell cover 2 so that as the reference cell cover 2 slideslaterally over the top of the reference cell panel 8 the fixed brush 4sweeps the surface of the reference cell panel 8.

Once the reference cell cover 2 is opened, exposing the reference cellpanel 8 to the sun, the measurement unit takes a measurement of thereference cell panel 8 and sends the measurement to the DAS and/orcommunications unit. The measurement may include Isc, Voc, Imp, Vmp, orany combination of these measurements.

The resulting measurement may be stored in the DAS and/or sent to aremote server via the communications unit.

After completing the measurement, a program stored in the MCU of the DASsends a signal to the motor controller 15 to close the reference cellcover 2. The inside sealing gasket 21 is mounted onto the reference cellcover 2 and the outside sealing gasket 22 is mounted on the referencecell panel 8 which is fixed (does not move), so that as the referencecell cover 2 moves laterally across the reference cell panel 8 theinside sealing gasket 21 slides along a grove provided by the outsidesealing gasket 22, which provides support to the reference cell cover 2as well as provide a hermetic seal between the reference cell cover 2and the top of the reference cell panel 8 when the reference cell cover2 is in the closed position.

Flexible PV Panel PCB

A flexible PCB 16 (FIGS. 6 and 7) provides a practical means forconnecting the plurality of PV cells in the soil monitoring panel 10 andreference cell panel 8 described in the previous disclosures, to themeasurement unit. During the construction of the soil monitoring panel10 and reference cell panel 8 the flexible PCB is laid on top of theseries connected PV cells and soldered to each of cell busbars 17. Theflexible PCB is an insulated, thin, flexible material which contains aprinted circuit designed to route the electrical connections from thebusbar of each PV cell on the soil monitoring panel 10 and referencecell panel 8 to the respective connections on the measurement unit.

The insulation on the flexible PCB ensures that the electrical leadsfrom each PV cell are safely routed to the respective pins on aconnector installed on the flexible PCB (FIG. 6, 7) which correspond tothe respective measurement unit connectors, without shorting otherportions of the PV panel cells or reference cell panel 8. The flexiblePCB is made of a compatible material to ensure that the PV panel EVA(insulation) and PV panel back sheet materials will adhere properlywhile being resistant to high temperatures required for the PV panellamination process. The flexible PCB ensures that each cell of the soilmonitoring panels and reference cell panel 8 is connected to theconnector pins in a precise and secure way.

In one embodiment, one set of connectors (plugs) are soldered directlyto the flexible PCB which is connected to the soil monitoring panel 10and reference cell panel 8. A second set of connectors (receptacles) isprovided on the electronic PCB's which are located in the electronicsenclosure 5 and which connect the flexible PCB, and therefore the PVcells of the soil monitoring panel 10 and reference cell panel 8 to themeasurement unit, charging system, and DAS.

Framing System

Edge soiling occurs when dirt pollen and mold accumulate at a border ofthe frame. The distance from the edge of the cell to the frame is notstandard further complicating the measurement of the effects of edgesoiling. This problem is solved in the present disclosure, by providinga superficial (i.e. does not provide a mechanical function to the soilmonitoring panel 10) frame 1 on the surface of the soil monitoring panel10 which is mechanically adjustable to match the precise distancebetween the frame and the boarder PV cells, of the native PV panels. Inthis way the present invention is able to precisely measure the effectsof edge soiling on standard PV panels.

The framing system, as shown in FIG. 2, may include separate framingpieces which are placed around the perimeter of the soil monitoringpanel 10 at a specific distance to the PV soil monitoring cells. Theframing pieces may be of any size or material and may be fixed to thesurface of the soil monitoring panel 10 glass using a standard adhesiveor common fastener to hold the framing pieces in place on the soilmonitoring panel 10.

Cleaning Cycle Calculation Predictive Software and Algorithms Summary

In one embodiment, the PV soil monitoring system as describedpreviously, may include a predictive software system (FIG. 8) toestimate an optimal time to clean the PV system. This application(referred to as the “PV clean cycle forecast tool”), is a web-basedsoftware tool that allows PV system investors, project managers, EPC's,developers and O&M contractors to estimate the optimal schedule, costsand frequency of panel cleaning that will be required for a particularPV plant.

In one embodiment the predictive software utilizes actual PV systemsoiling loss measurements, first year hourly, PV system performancereports, and TMY weather datasets to calculate the estimated soilinglosses. The cost of energy lost due to soiling is calculated at eachhourly output and compared with the costs of cleaning the panels. Theoptimal time to clean is exactly when the cost of the loss of energy dueto soiling becomes more than the cost of cleaning the panels, within aspecified soiling period.

In a second embodiment, a near-term forecast application calculates thenext optimal clean of the PV system using actual soiling measurementsfrom the previously described PV soil monitoring system as well asnear-term weather forecasts, energy output forecasts to determineoptimal time to clean the PV panels.

To calculate the optimal time to clean the PV panels, a window of time,the soiling period, is defined as a function of the soiling rate. Thesoiling period is the time it takes for the accumulation of soiling toreturn to the same percentage before cleaning.

For the initial period the soiling period is the time it takes for thesoiling to reach the maximum soiling loss percentage. For subsequentperiods, the soiling period is calculated based-on the forecast soilingrate for the next period, starting from the point of the previouscleaning event (manual or rainfall).

The maximum soiling percentage is defined as the maximum percentage ofloss of the PV irradiance due to soiling. As the soiling accumulates onthe surface of the PV panels it generally forms layers. The soilingaccumulation in general tends to be fairly linear (barring any unregularsoiling events such as muddy rain and sandstorms), and tends tolevel-off to a near 0 accumulation rate over time. This is due to thefact that soiling accumulates on top of existing soiling layers and hasonly a very minimal effect in further losses to transperancy of thelight passing through.

In order to calculate if and when the investment will pay off within agiven soiling period, the cost of the loss of energy due to soilingequivalent to the cost of cleaning is calculated. If the cost of theloss of energy due to soiling equals the cost of cleaning within thesoiling period, then a cleaning event is marked on a calendar at thebeginning of the period. However, if the cost of the loss of energy doesnot equal the cost of cleaning within the given soiling period, then theentire soiling period is incremented forward by one unit of time (i.e.one hour) and do the same calculation until the cost of the loss ofenergy due to soilinge equals the cost of cleaning within the calculatedsoiling period.

The cleaning will never be optimal before the cost of the loss of energydue to soiling equalling the cost of cleaning. At the same time it wouldneed to be determined if the system should be cleaned by determiningwhether an investment into cleaning the panels will pay off in the nextperiod. The soiling rate and therefore the soiling period is alwayschanging. The production of energy is also changing within each period,which is a determining factor for whether or not a given cleaning eventwill pay off within a given soiling period.

It may be required to look into the future to determine if a cleaningevent will make sense. First the soiling loss is accumulated and theresulting energy loss beginning at the point when the cost of the lossequals cost of cleaning for the previous period (which defines thebeginning of the next soiling period), moving forward until we reach theend of the soiling period or until the point where the cost of the lossequals the cost of cleaning is reached, whichever comes first. If thecost of the loss equals the cost of cleaning within the soiling period(before reaching the end of the soiling period) the clean cycle calendaris marked to indicate a required cleaning event for this date. Thecleaning event also marks the beginning of the next soiling period.

If, however, the end of the soiling period is reached, before reachingthe point Where the cost of loss equals the cost of cleaning, the entiresoiling period is incremented forward by one unit (i.e. one hour) andrecalculated to determine if the cost of the loss will equal the cost ofcleaning within the new soiling period. Note that the soling rate maychange after incrementing the period and therefore the length of thesoiling period would also change in the case that a change in thesoiling rate happens after incrementing the period (i.e. the soilingperiod is incremented to the next monthly soiling rate).

The cleaning event will coincide with the pay-off point (when the costof loss equals cost of cleaning) of the previous period when the soilingrate, max soiling loss percentage and energy production are the same asthe previous period.

The method disclosed herein and shown in FIG. 8 relies on the on-sitemeasurements of the PV soil monitoring system to accurately determinethe characteristic soiling of a PV system. Using the cell-levelmeasurements described previously over time can provide the requireddata to help predict the soiling rate and associated soiling period fora given PV plant with a high level of accuracy and reliability. Inaddition, the soiling rate system design details (i.e. elevation angle,orientation, type of mounting system . . . etc.) and near and long-termweather forecasts are used to determine the probabilities of a cleaningevent occurring within specified soiling period.

With the advent of machine learning, a predictive model for soiling canbe built from the on-site soiling measurements of said PV soilmonitoring system hardware, which can produce highly accurate andreliable forecasts of the soiling rate and soiling period for a given PVsystem.

At different incident angles/times of day, the effects of soiling changedue to internal reflections and shading effects (as the angles arelonger the effects of soiling are greater). In addition to modelingsoiling rates based on cross-correlations of weather data (i.e. wind andrelative humidity) and environmental data (i.e. foundation, environment,etcc), the calculation may also include the time of day and latitude ofthe site in order to calculate the losses due to incident angle of thesun.

These general algorithms are used in both the annual PV clean cycleforecast tool, and a 7-day forecast tool. In the case of the 7-dayforecast tool, the system utilizes actual soiling rates calculated fromonsite measuring units which measure the amount of soiling loss for aspecific site. This data is then uploaded to a web server where it isused to calculate the soiling period and associated forecast of cleaningfor a given period ongoing. The list of inputs to the 7-day forecasttool is below, however users will input the required information onlyonce and the 7-day forecast tool will automatically provide an updatedclean cycle calendar calculated from the updated site soilingmeasurements each time a user logs into the web monitoring portal.

In one embodiment, an annual clean cycle forecast tool, may include asoiling rate calculator to help users estimate the site-specific soilingrates, in the case that the site specific soiling rates are not wellknown. The soiling rate calculator, is designed to help users calculatean approximate the soiling rate based-on PV system design, technology,and environmental factors. In addition, the soiling rate calculator, mayutilize datasets collected from a database of customer sites and on-sitemeasurements of soiling rates using the PV soil monitoring systems, tohelp estimate the site-specific soiling rates and soiling period,based-on site specific information. The soiling rate calculator, resultsin an average soiling rate per specified period (i.e. per month), foreach month of the year, which users can further modify.

Similarly, a near-term forecast (i.e. 7-days in advance) tool utilizesactual site soiling measurements to predict the future soiling rates andthe soiling period, using a cross correlation of sites specific weatherdata (i.e. relative humidity, temperature, precipitation, windspeed,etc.) and soiling measurements.

The calculations require the summation of energy produced from the PVsystem over the specified period of time. In the case of the 7-dayforecast tool, the actual energy production may be used in thecalculation; in the annual clean cycle forecast tool, an annualapproximation of the energy production for the plant is calculated usinga PV performance modeling tool (i.e. PV system, PVWATTS . . . etc).

The energy and associated losses due to soiling are calculated andsummed over the soiling period until either 1) a rainfall event or 2) amanual clean event occur within the given soiling period. If the amountof rainfall in a single hour exceeds the user specified threshold(mm/hr) the panels are considered cleaned, the soiling rate is set to0%, and a rainfall clean event is noted on the schedule. A rainfallevent that is less than the specified amount results in a reduction inthe accumulated soiling % by a ratio of the amount of rainfall(mm/hr)/rainfall clean amount (mm/hr).

The hourly accumulated soiling loss percentage is multiplied by thetotal energy produced per hour to calculate the sum the energy lost dueto soiling until a “cleaning event” (rainfall or panel cleaning) withinthe given soiling period sets the summation back to 0 or a calculatedratio of the accumulated soiling % (in the case of a rain event lessthan the rainfall clean amount). Additional weather factors such as thewind speed and direction, relative humidity, type of foundation/soiling,panel angle of installation, rainfall, may also be considered whencalculating the soiling rate on an hourly basis.

The cost of the loss of energy due to accumulated soiling is comparedwith the cost of cleaning at each hour throughout the first year todetermine the optimal frequency and schedule for cleaning, over thefirst year.

In the case that the soiling level results in a total energy productionloss and cost of energy loss, which is greater than the cost of cleaningthe panels, within a given soiling period then a panel cleaning isscheduled for that day or days required to clean the PV system.

The amount of time required for the soiling to stabilize or reach themaximum soiling loss percentage or return to the previous level before aclean event, is the soiling loss period. It is the job of the PV cleancycle forecast tool and 7-day forecast tool, to determine if a futureinvestment in cleaning will pay off within this soiling period.

Physically the soiling losses can be measured using an on-site PV soilmonitoring system as described here previously and verify if therelevant predictions were correct and calculate how much was gained fromthe investment in cleaning. If the cost of the loss of energy due tosoiling is greater than or equal to the cost of cleaning the PV system,within this soiling loss period, then the investment in cleaning paysoff. If the cost of the loss of energy due to soiling is less than thecost of cleaning the PV system during the soiling period, Then the userlost money from the investment in cleaning the PV system.

The correct algorithm therefore, should account for the future soilingrate, by defining the soiling period and determining whether or not aninvestment into cleaning will pay off during this period. If theinvestment into cleaning the PV system is not predicted to pay off in agiven soiling period, Then, the soiling period should be incremented byone-time unit (i.e. one hour) (i.e. the same soiling period, projected 1hour later), until a clean event is triggered within the soiling period.

The output report provides users an annual calendar (365 days) wherecleaning events are noted (natural events are in green, scheduledcleanings are in red) for each day of the year. Other information suchas, total estimated cost of cleaning, total amount of energy lost due tosoiling, total cost of energy lost due to soiling, average soiling losspercentage, and total number of cleanings are displayed in theresulting, clean cycle calendar.

PV system performance datasets and weather datasets may be saved so thatthe model can be re-run using different user inputs.

In another embodiment the PV clean cycle forecast tool may be configuredso as to calculate a maximum soiling loss percentage for a given PVsystem. In this case the forecast tool will use the max soiling losspercent (instead of cost of the loss of energy) to determine when toclean the panels. When the accumulated soiling loss is greater than orequal than the mass soiling loss percent specified by the user, a manualclean is triggered and marked on the clean cycle calendar. The toolresults will specify the cost of cleaning, cost of soiling loss, totalenergy lost and the estimated average soiling percent.

In yet another embodiment the PV clean cycle forecast tool can beconfigured, to calculate the soiling loss based-on a specified cleaningcycle. In this case the user selects the days to clean from aninteractive calendar and the tool calculates the resulting soiling losspercentage for the year, cost of soiling loss, and cost of cleaninggiven the selected cleaning cycle.

There are two forecast tools presented here with slightly differentalgorithms. The PV clean cycle forecast tool is a near term predictivetool that utilizes actual soiling rates and near term weather forecaststo determine the soiling window (as described above).

PV Clean Cycle Calendar Predictive Software Detailed Descriptions

The PV clean cycle calendar is a near-term (i.e. 7-day) forecast whichdetermines when will be the next optimal time to clean the PV panels.

In one embodiment, the near-term (i.e. 7-day) predictive software maycalculate the optimal cleaning cycle. The required datasets and userinputs may include:

-   -   1. DC power produced per the time unit defined (i.e. hours) for        all or a portion of the PV system        -   i. The ACTUAL energy production datasets are used to verify            the economics of the cleaning investment (i.e. did cleaning            the PV system pay off during the last soiling period).            -   1. This dataset may be derived from regular logs of a                single PV string within a PV system or alternatively may                be parsed from a third-party monitoring report, or                directly uploaded from a third-party monitoring system.        -   ii. The FORECASTED energy production datasets are used to            predict when the cost of cleaning=the cost of loss of energy            due to soiling for the Soiling Period            -   1. This dataset may be derived from an energy modeling                tool such as PVSYST or PVWATTS or alternatively may be                derived from system design inputs and local weather                forecasts.    -   2. Actual Soiling measurements from Soil Monitoring System        -   i. This dataset is used to calculate regression coefficients            to predict the near-term soiling rates and soiling window.            -   1. The dataset may include time stamps to calculate the                incident angle of the sun and its effects on soiling                throughout the day.    -   3. Near-term (i.e. 7-day) local weather forecast        -   i. This dataset may be obtained from a third-party API or            alternatively may be gathered by onsite weather sensors for            near term predictions of local weather.    -   4. The following inputs may be used to collect information used        to calculate user specific data:        -   i. Location of Plant (state, city, street, zip)        -   ii. DC System Size (kWp)        -   iii. AC Inverter Max Output Rating (kWp)            -   1. This dataset is used to calculate inverter clipping        -   iv. Module Type: (Poly, Mono, Thin film)        -   v. Array Type: (Roof, Ground Fixed, Ground 1-Axis Tracking,            Ground 2-Axis Tracking)            1. Panel Tilt (degrees): (0-90)            2. Azimuth (Degrees): (0-360): 0 degrees is North.

3. Advanced Parameters: (DC to AC Size Ratio, Inverter Efficiency)

PV Annual Clean Cycle Calendar Algorithms and Datasets

-   -   1. After constructing the weather and energy output data files        (.csv), we use the weather adjusted Soiling Rate from the PV        Soil Monitoring System (i.e. Characteristic soiling patterns        correlated with locally forecasted weather) to determine the        Soiling Period (the time it takes for the soiling to return to        the previous soiling loss %). For the initial period the Soiling        Period may be defined as the time it takes to reach the Maximum        Soiling Loss %.    -   2. The Soiling Loss % is calculated by measuring the soiling        loss from the Soil Monitoring system as described above. A        regression model based-on the actual soiling measurements from        the previous period may be used to calculate the soiling window        (soiling rate defined from the time of clean panels to the        moment of the max soiling loss) for the next period.    -   3. The Soiling Loss % is calculated for each time increment        (i.e. hourly) into the future, by incrementing the defined        Soiling Rate % which is added to the previous soiling loss % for        the previous time instant (i.e. Previous hour).    -   4. The Amount of Energy Lost due to soiling for each time unit        (i.e. each hour), is calculated by multiplying the DC Power        Output (Watts)*the soiling loss % to get the Total Power (Watts)        Lost per time period (i.e. hour).    -   5. After calculating the Total Power (Watts) Lost per hour, we        use the user input Price of Energy*Total Energy Lost Due to        Soiling, to get the Total Cost of Energy Lost per time period        (i.e. hourly)    -   6. If the amount of precipitation in the weather forecast        is >=the Rainfall Clean Amount (mm) calculated by the AI        (machine learning from previous events), then the Soiling Loss %        is reset to 0%, and the calendar is marked with a Rainfall Clean        Event. If there is a Rainfall event which is <the Rainfall Clean        Amount, then the Accumulated Soiling % is adjusted by the ratio        of the Rainfall Amount (mm/hr)/Rainfall Clean Amount according        to the previously characterized rainfall events in the soiling        database.    -   7. Inverter Saturation—in the case where inverters are sized        significantly less than peak power of the PV system, the        inverter saturation is considered by eliminating any power lost        to soiling that will result in a power production over the        inverter rated DC capacity.    -   8. If the Total Cost of Energy Lost is <the Total Cost of        Cleaning ($/kWp) AND the amount of precipitation is <the        Rainfall Clean Amount, AND the total power production is under        the inverter saturation limit, then we add the Total Cost of        Energy Lost from the previous hour to the Total Cost of Energy        Lost for the present hour.    -   9. The Total Cost of Energy Lost is summed over the forecasted        Soiling Period until 1) the end of the Soiling Period has been        reached OR 2) the Total Cost of Energy Lost is >=the Cost of        Cleaning (user input).        -   i. IFF the end of the Soiling Period has been reached we            increment the time to the Soiling period by one-time unit            (i.e. One hour) and repeat steps C, D, and E.        -   ii. IFF the Total Cost of Energy Lost is >=the Cost of            Cleaning (user input) within the defined Soiling Period,            then we set the Soiling Loss % to 0 and mark the dataset            with a Manual Cleaning Event.    -   10. Days to Clean—in the case of a Manual clean event (the Cost        of Soiling Loss is >=Cost of Cleaning, we have to proportion the        number of days it takes to clean the system (eg. If user inputs        10 days to clean the panels we clean 1/10 of the panels each day        for 10 days). The remaining panels that are not cleaned will        continue to loss energy at the summed rate, while those that        were just cleaned the Total Soiling Loss % will be set back to        monthly soiling rate.    -   11. The measured soiling rate and accumulated soiling losses are        measured using on-site soil monitoring system (as described        above). Cleaning Cycles, Soiling Losses and Soiling rates are        measured and confirmed by the on-site soiling measurements.    -   12. The Manual Clean Events will be saved in an array and output        on a yearly calendar    -   13. The Rain Clean Events will be saved in an array and output        on a yearly calendar    -   14. The total cost of cleaning (for the next and/or previous        period) will be summed and output    -   15. The total cost of soiling loss (for the next and or previous        period) will be summed and output    -   16. The average soiling loss % (for the next and or previous        period) will be summed and output. The user will have the option        to re-run the calculation using different values for Cost of        Cleaning, Cost of Energy, Average Monthly Soiling Loss % (per        month), Days to Clean, and Rainfall Clean Amount (mm).

The output of the Clean Cycle Calendar may be presented in a monthly orweekly calendar and/or report that displays one or more of the followinguser outputs:

-   -   1. Cost of Cleaning    -   2. Cost of Soiling Loss    -   3. Manual Cleaning event (estimated day to clean using manual        cleaning techniques)    -   4. Rainfall clean event (estimated clean by rainfall)    -   5. Sandstorm (estimated sand storm)    -   6. Muddy Rainfall event (estimated dirty rain which will dirty        the panels)

Annual Clean Cycle Forecast Tool

The Annual Clean Cycle Forecast Tool is a predictive software tool thatis used to estimate the soiling losses, frequency of cleaning and costsfor a given PV system.

There may be three different configurations (algorithms) for running theAnnual Clean Cycle Forecast tool. These include:

-   -   1. Calculate the Optimal Clean Cycle    -   2. Calculate the Clean Cycle based-on a specified Soiling Rate    -   3. Calculate the Soiling Rate based-on the Clean Cycle

After selecting one of the options above the software may calculate twodatasets (required for all three embodiments above):

-   -   1. The hourly first year energy output (DC Watts) 8760 .csv        -   i. This dataset may be calculated using the NREL performance            calculator (PV Watts) or similar PV performance modeling            software.    -   2. The hourly first year TMY weather dataset .csv (or other data        formats).        -   i. This dataset will be calculated using an API where users            can specify location data and retrieve an hourly weather            dataset    -   3. First Year Soiling Rate        -   i. This dataset may be calculated using actual soiling            measurements which closely correspond to the PV system            design, location, environmental and weather specific data.        -   ii. The software may use a regression model to calculate            future soiling rates based-on actual soiling rates and cross            correlated weather data, system design and environmental            conditions.

Using the required PV system information we first calculate the HourlyFirst Year Energy Output from a specified PV performance modellingapplication and fetch and save the resulting DC Energy Output

-   -   1. The following inputs page may be used to collect information        used to calculate the Energy Output Dataset (PV Watts):        -   i. Location of Plant (state, city, street, zip)        -   ii. DC System Size (kWp)        -   iii. Module Type: (Poly, Mono, Thin film)        -   iv. Array Type: (Roof, Ground Fixed, Ground 1-Axis Tracking,            Ground 2-Axis Tracking)        -   v. System loss % (see Loss Calculator PV Watts)        -   vi. Panel Tilt (degrees): (0-90)        -   vii. Azimuth (Degrees): (0-360): 0 degrees is North.        -   viii. Advanced Parameters: (DC to AC Size Ratio, Inverter            Efficiency)    -   2. Next calculate the Hourly First Year Weather Data        (precipitation, wind speed, RH) from the weather API and save        the (ie. hourly .csv) file.        -   i. For the Weather Dataset only the location (lat/long) will            be required.    -   3. Using the weather dataset and PV system design and location        inputs, a soiling rate dataset is calculated for the first year        of operation.        -   i. A soiling rate calculator may be provided to help users            determine the soiling rate based-on the specific design and            location of the pv system (see Soiling Rate Calculator            section below).

In one embodiment, the Annual PV Clean Cycle Predictive Software mayCalculate Optimal Cleaning Cycle, (User may also choose to Upload aPVSYST .csv file or similar file).

The following user inputs may be required:

-   -   1. Average Monthly Soiling Rate % (see Soiling Rate Calculator)    -   2. Module Frame Type: (Framed, Frameless)    -   3. Rainfall Clean amount (mm)    -   4. Max Cumulative Soiling Loss %    -   5. Sandstorm Events calendar    -   6. Muddy Rain Event Periods    -   7. Currency (Euro/$)    -   8. Average Cost of Cleaning ($/kWp/yr)    -   9. Average Cost of Energy ($/kWh)    -   10. Cleaning Duration (number of days required to clean the        entire plant) (1-30 days)    -   11. Cleaning Cycle Start Date (day to begin cleaning cycle)

After constructing the weather and energy output data files (.csv), weuse the weather adjusted Soiling Rate from the PV Soil Monitoring System(i.e. characteristic soiling patterns correlated with locally forecastedweather) to determine the Soiling Period (the time it takes for thesoiling to return to the previous soiling loss %). For the initialperiod the Soiling Period may be defined as the time it takes to reachthe Maximum Soiling Loss %.

The Soiling Loss % for each time increment (i.e. hourly) is incrementedby the defined Soiling Rate % which is added to the previous soilingloss % for the previous time instant (i.e. Previous hour).

The Amount of Energy Lost due to soiling for each time unit (i.e. Eachhour), is calculated by multiplying the DC Power Output (Watts)*thesoiling loss % to get the Total Power (Watts) Lost per time period (i.e.hour).

After calculating the Total Power (Watts) Lost per hour, we use the userinput Price of Energy*Total Energy Lost Due to Soiling, to get the TotalCost of Energy Lost per time period (i.e. hourly)

If the amount of precipitation in the weather forecast is >=the RainfallClean Amount (mm) calculated by the AI (machine learning from previousevents), then the Soiling Loss % is reset to 0%, and the calendar ismarked with a Rainfall Clean Event. If there is a Rainfall event whichis <the Rainfall Clean Amount, then the Accumulated Soiling % isadjusted by the ratio of the Rainfall Amount (mm/hr)/Rainfall CleanAmount according to the previously characterized rainfall events in thesoiling database.

Inverter Saturation—in the case where inverters are sized significantlyless than peak power of the PV system, the inverter saturation isconsidered by eliminating any power lost to soiling that will result ina power production over the inverter rated DC capacity. If the TotalCost of Energy Lost is <the Total Cost of Cleaning ($/kWp) AND theamount of precipitation is <the Rainfall Clean Amount, AND the totalpower production is under the inverter saturation limit, then we add theTotal Cost of Energy Lost from the previous hour to the Total Cost ofEnergy Lost for the present hour.

The Total Cost of Energy Lost is summed over the Soiling Period until 1)the end of the Soiling Period has been reached OR 2) the Total Cost ofEnergy Lost is >=the Cost of Cleaning (user input).

-   -   1. IFF the end of the Soiling Period has been reached we        increment the beginning of the Soiling period (i.e. The time        when the Soiling Period starts) by one-time unit (i.e. one hour)        and repeat steps C, D, and E.    -   2. IFF the Total Cost of Energy Lost is >=the Cost of Cleaning        (user input) within the defined Soiling Period, then we set the        Soiling Loss % to 0 and mark the dataset with a Manual Cleaning        Event.

Days to Clean—in the case of a Manual clean event (the Cost of SoilingLoss is >=Cost of Cleaning, we have to proportion the number of days ittakes to clean the system (eg. If user inputs 10 days to clean thepanels we clean 1/10 of the panels each day for 10 days). The remainingpanels that are not cleaned will continue to loss energy at the summedrate, while those that were just cleaned the Total Soiling Loss % willbe set back to monthly soiling rate.

The Manual Clean Events will be saved in an array and output on a yearlycalendar

The Rain Clean Events will be saved in an array and output on a yearlycalendar

The total cost of cleaning (first year) may be summed and outpu.

The total cost of soiling loss (first year) may be summed and output.

The average soiling loss % (first year) may be summed and output.

The user may have the option to re-run the calculation using differentvalues for Cost of Cleaning, Cost of Energy, Average Monthly SoilingLoss % (per month), Days to Clean, and Rainfall Clean Amount (mm).

In another embodiment the Annual PV Clean Cycle Predictive software mayCalculate the Cleaning Cycle required to maintain a Maximum soiling loss%.

The following user inputs may include:

-   -   1. Average Soiling Rate % per month (see Soiling Rate        Calculator)    -   2. Module Frame Type: (Framed, Frameless)    -   3. Rainfall Clean amount (mm)    -   4. Max Cumulative Soiling Loss %    -   5. Sand Storm Events Calendar    -   6. Muddy Rainfall Event Periods    -   7. Currency (Euro/$)    -   8. Average Cost of Cleaning ($/kWp/yr)    -   9. Average Cost of Energy ($/kWh)    -   10. Cleaning Duration (number of days required to clean the        entire plant)    -   11. Cleaning Cycle Start Date (day to begin cleaning cycle)

After constructing the weather and energy output data file we use theuser input Monthly Soiling Rate accumulated over the specified timeperiod to determine the Amount of Energy Lost, by multiplying the EnergyOutput (Watts)*the hourly soiling loss % (derived from the monthlyaverage Soiling Loss %) to get the Total Watts Lost (per hour).

After calculating the Total Watts Lost per hour, we use the user inputCost of Energy*Total Watts Lost to get the Total Cost of Energy Lost perhour.

If the Max Allowable Soiling Loss % (use input)>=Soiling Loss % (this iscalculated as the hourly cumulative soiling loss percent) we set theSoiling Loss % to 0 and mark the dataset with a Manual Cleaning Event.OR if the amount of precipitation in the weather dataset is >=theRainfall Clean Amount (mm) input by the user, then the Soiling Loss % isset back to 0 and we mark the dataset with a Rainfall Cleaning Event. Ifthere is a Rainfall event which is <the Rainfall Clean Amount, then theAccumulated Soiling % is adjusted by a ratio of a Rainfall Amount(mm/hr)/Rainfall Clean Amount.

If there is a Rainfall event which is <the Rainfall Clean Amount, thenthe Accumulated Soiling % is adjusted by the ratio of the RainfallAmount (mm/hr)/Rainfall Clean Amount.

The Amount of Energy Lost Due to Soiling is determined by multiplyingthe Accumulated Soiling % by the Total Power Produced by the PV systemfor each hour of the performance output (8760, .csv).

Inverter Saturation—in the case where inverters are sized significantlyless than peak power of the PV system, the inverter saturation isconsidered by eliminating any power lost to soiling that will result ina power production over the inverter rated DC capacity.

If the Total Cost of Energy Lost is <the Total Cost of Cleaning ($/kWp)AND the amount of precipitation is <the Rainfall Clean Amount, then weadd the Total Cost of Energy Lost from the previous hour to the TotalCost of Energy Lost for the present hour.

Days to Clean—in the case of a Manual clean event (the Cost of SoilingLoss is >=Cost of Cleaning, we have to proportion the number of days ittakes to clean the system (e.g. If user inputs 10 days to clean thepanels we clean 1/10 of the panels each day for 10 days). The remainingpanels that are not cleaned will continue to loss energy at the summedrate, while those that were just cleaned the Total Soiling Loss % willbe set back to monthly soiling rate.

The Manual Clean Events will be saved in an array and output on a yearlycalendar.

The Rain Clean Events will be saved in an array and output on a yearlycalendar.

The total cost of cleaning (first year) will be summed and output.

The total cost of soiling loss (first year) may be summed and output.

The average soiling loss % (first year) may be summed and output.

The user may have the option to re-run the calculation using differentvalues for Cost of Cleaning, Cost of Energy, Average Monthly SoilingLoss % (per month), Days to Clean, and Rainfall Clean Amount (mm).

In another embodiment the Annual PV Clean Cycle Predictive software mayCalculate the Cleaning Cycle based-on a specific cleaning schedule.

The following user inputs may include:

-   -   1. Cleaning Cycle (the dates to clean should be selectable from        a calendar graphic)    -   2. Average Soiling Rate % per month (see Soiling Rate        Calculator)    -   3. Module Frame Type: (Framed, Frameless)    -   4. Rainfall Clean amount (mm)    -   5. Max Cumulative Soiling Loss %    -   6. Sand Storm Event Calendar    -   7. Muddy Rainfall Event Periods    -   8. Currency (Euro/$)    -   9. Average Cost of Cleaning ($/kWp/yr)    -   10. Average Cost of Energy ($/kWh)    -   11. Cleaning Duration (number of days required to clean the        entire plant)

After constructing the weather and energy output data file (.csv), theuser inputs Monthly Soiling Rate accumulated over the time period todetermine the Amount of Energy Lost each hour, by multiplying the EnergyOutput (Watts)*the hourly soiling loss % (derived from the monthlyaverage Soiling Loss %) to get the Total Watts Lost (per hour).

After calculating the Total Watts Lost per hour, the user input Cost ofEnergy*Total Watts Lost is used to get the Total Cost of Energy Lost perhour.

If the Day of Cleaning is marked on the Calendar (user input) theSoiling Loss percentage is set to 0 and mark the dataset with a ManualCleaning Event or if the amount of precipitation in the weather datasetis >=the Rainfall Clean Amount (mm) input by the user, then the SoilingLoss % is set back to 0 and the dataset is marked with a RainfallCleaning Event. If there is a Rainfall event which is <the RainfallClean Amount, then the Accumulated Soiling % is adjusted by the ratio ofthe Rainfall Amount (mm/hr)/Rainfall Clean Amount.

If there is a Rainfall event which is <the Rainfall Clean Amount, thenthe Accumulated Soiling % is adjusted by the ratio of the RainfallAmount (mm/hr)/Rainfall Clean Amount.

The Amount of Energy Lost Due to Soiling is determined by multiplyingthe Accumulated Soiling % by the Total Power Produced by the PV systemfor each hour of the performance output (8760, .csv).

Inverter Saturation—in the case where inverters are sized significantlyless than peak power of the pv system, the inverter saturation isconsidered by eliminating any power lost to soiling that will result ina power production over the inverter rated DC capacity.

If the Total Cost of Energy Lost is <the Total Cost of Cleaning ($/kWp)AND the amount of precipitation is <the Rainfall Clean Amount, then theTotal Cost of Energy Lost from the previous hour is added to the TotalCost of Energy Lost for the present hour.

Days to Clean—in the case of a Manual clean event (the Cost of SoilingLoss is >=Cost of Cleaning, the number of days it takes to clean thesystem must be proportioned (e.g. if user inputs 10 days to clean thepanels we clean 1/10 of the panels each day for 10 days). The remainingpanels that are not cleaned will continue to loss energy at the summedrate, while those that were just cleaned the Total Soiling Loss % willbe set back to the monthly soiling rate.

The Manual Clean Events will be saved in an array and output on a yearlycalendar.

The Rain Clean Events will be saved in an array and output on a yearlycalendar. The total cost of cleaning (first year) may be summed andoutput.

The total cost of soiling loss (first year) may be summed and output.

The average soiling loss % (first year) may be summed and output.

The user will have the option to re-run the calculation using differentvalues for Cost of Cleaning, Cost of Energy, Average Monthly SoilingLoss % (per month), Days to Clean, and Rainfall Clean Amount (mm).

Soiling Rate Calculator

In one embodiment the PV Clean Cycle predictive software may include aSoiling Rate Calculator. The Soiling Rate Calculator part of the PVClean Cycle Forecast tool and is intended to help users estimate therate of soiling accumulation for the PV system. Soiling rates are highlydependent on technology, design and location, and therefore will varywidely for each PV system. The Soiling Rate Calculator is an optionalcalculator that is integrated into the Web-Based, PV Clean CycleForecast Tool.

In one embodiment of the Soiling Rate Calculator, the user may bepresented with some additional inputs, including but not limited to:

-   -   1. Type of Panel Frame (Framed/Frameless)    -   2. Type of foundation (Grass, gravel, dirt, sand, TPO/PVC,        ModBit, Water)    -   3. Environmental Factors (Surronding Trees/Pollen, Nearby        Factories/Smog,

Nearby Highway, Nearby Ocean, Neaby Farm, Desert)

Previously inputted data from the PV Clean Cycle Forecast Tool form, mayalso be used in the calculation of the Soiling Rate including:

-   -   1. Location of the PV System    -   2. Tilt Angle of the PV panels    -   3. Array Type (fixed (open rack), Fixed (roof mount), SAT, SAT        (Backtracking), 2-Axis tracking)    -   4. Module Type (Polycrystaline, Monocrystaline, Thin Film)

Additionally, a Soiling Rate database derived from the data collectedfrom customer sites, may be used to match corresponding design,technology, and location data in order to calculate the most appropriateSoiling Rates for each period.

After clicking the Calculate button, the Monthly Average Soiling Ratesfor each month of the year are populated, in the PV Clean Cycle ForecastTool. Users may choose to further modify any of the values.

The foregoing description of preferred embodiments of the presentdisclosure has been presented for purposes of illustration anddescription. The described preferred embodiments are not intended to beexhaustive or to limit the scope of the disclosure to the preciseform(s) disclosed. Obvious modifications or variations are possible inlight of the above teachings. The embodiments are chosen and describedin an effort to provide the best illustrations of the principles of thedisclosure and its practical application, and to thereby enable one ofordinary skill in the art to utilize the concepts revealed in thedisclosure in various embodiments and with various modifications as aresuited to the particular use contemplated. All such modifications andvariations are within the scope of the disclosure as determined by theappended claims when interpreted in accordance with the breadth to whichthey are fairly, legally, and equitably entitled.

What is claimed is:
 1. A solar panel cleaning system comprising: an automated cleaning device for cleaning a surface of a reference cell panel; a cleaning device controller in communication with a motor of the automated cleaning device, the cleaning device controller configured to receive a signal corresponding to measurement of a current of photovoltaic system; wherein the cleaning device controller activates the automated cleaning device to clean a surface of the reference cell panel when the received signal indicates that a measurement of the current of the photovoltaic system is to be taken.
 2. The solar panel cleaning system of claim 1, the automated cleaning device further comprising a reference cell cover that is movable between open and closed positions, wherein in a closed position the reference cell cover substantially protects the surface of the reference cell panel.
 3. The solar panel cleaning system of claim 2, the reference cell cover further comprising a brush attached to the reference cell cover for cleaning the surface of the reference cell panel when the reference cell cover moves between open and closed positions.
 4. The solar panel cleaning system of claim 3, further comprising a moisture sensor located adjacent the reference cell panel.
 5. The solar panel cleaning system of claim 2, wherein the reference cell cover is slidably associated with the reference cell panel such that the reference cell cover slides between open and closed positions to protect the surface of the reference cell panel.
 6. The solar panel cleaning system of claim 5, further comprising a linear motor in communication with the reference cell cover for sliding the reference cell cover between open and closed positions.
 7. The solar panel cleaning system of claim 6, the linear motor comprising a drive screw engaged with a drive screw bar that is attached to the reference cell cover to move the reference cell cover between open and closed positions.
 8. The solar panel cleaning system of claim 2, further comprising an electronics enclosure housing a motor controller and a motor for moving the reference cell cover between open and closed positions.
 9. The solar panel cleaning system of claim 1, wherein reference sell panel is connected to a printed circuit board.
 10. The solar panel cleaning system of claim 1, further comprising a data acquisition system (DAS) for sending instructions to the automated cleaning device to measure the short circuit current of the reference cell panel and receiving data corresponding to the photovoltaic system.
 11. The solar panel cleaning system of claim 10, further comprising a soiling loss module operable on the data acquisition system for determining an amount of soiling loss based on measured short circuit currents of panels of the photovoltaic system and the reference cell panel.
 12. The solar panel cleaning system of claim 1, wherein the reference cell panel shares a glass substrate with a soil monitoring panel of the photovoltaic system.
 13. The solar panel cleaning system of claim 2, further comprising one or more gaskets between the reference cell cover and the reference cell panel.
 14. The solar panel cleaning system of claim 1, wherein the reference cell panel and soil monitoring panels are installed co-planar to the photovoltaic system.
 15. A solar panel cleaning system comprising: an automated cleaning device for cleaning a surface of a reference cell panel; a cleaning device controller in communication with a motor of the automated cleaning device, the cleaning device controller configured to receive a signal corresponding to measurement of a current of photovoltaic system; a reference cell cover that is movable between open and closed positions, wherein in a closed position the reference cell cover substantially protects the surface of the reference cell panel; wherein the cleaning device controller activates the automated cleaning device to clean a surface of the reference cell panel when the received signal indicates that a measurement of the current of the photovoltaic system is to be taken. 